Rotor blades are mounted on the periphery of a turbine rotor disc by profiled blade roots fitted into corresponding slots in the rotor disc. The profile takes up the radially directed forces occurring during the operation of a gas turbine.
When mounted in essentially axial slots a locking feature is required to prevent the blade roots from moving in the slots during operation, due to gas load.
One arrangement known from the state of the art is to use segmental plates fitted between blade roots and rotor disc and mounted in respective annular grooves in the blade roots and the rotor disc to provide axial retention. Such an arrangement usually only allows for small manufacturing tolerances since it is important that the loading due to the centrifugal forces of the locking plates onto the blades above it and the damping of blade vibrations through the locking plates is consistent. The locking plates must be free to articulate to cope with deviations in manufacturing tolerances of the grooves in the disc, holding the plates, the deviations causing a radial or rotational movement of the plate.
Furthermore a compromise must be found for the size of the gap space between locking plates. On the one hand, if gap spaces between locking plates are too narrow, they will lock up during the start-up phase. Due to the low thickness of the locking plates compared to the rotor disc and the rotor blades, the thermal inertia of the locking plates is smaller and thus their thermal expansion is quicker than for the rotor disc and the rotor blades. On the other hand, if gap spaces between locking plates are wide, sealing between blade roots and rotor disc and between blades is poor.
GB 2 258 273 A describes a rotor blade locking assembly having plates trapped between retaining hooks integral with rotor disc and blade roots. The plate covers and seals the space between blade roots and rotor disc.
EP 1 657 404 A1 describes a rotor of gas turbine having the rotor blades anchored by in axial slots in the body of the rotor and secured by locking plates. The locking plates have a kite-like and especially a parallelogram or rhomboid-like base contour and are fitted in a position between the rotor body and rotor blades and then in an assembly position rotated relative to the inserted position into the annular grooves formed in the rotor body and in the blades.